The Internet of Things (IoT) is “the Internet connecting things”, and the Internet of Things extends a client scope of the Internet to articles for information exchange and communication. This communication mode is also referred to as machine type communication (MTC), and a communications node in this communication mode is referred to as an MTC terminal. A typical application of the Internet of Things includes smart metering, smart household, and the like. Because the Internet of Things needs to be applied to various scenarios such as outdoor, indoor, and underground environments, many special requirements are imposed on design of the Internet of Things.
First, the Internet of Things needs to have relatively good coverage performance. Many MTC devices such as a meter and a water meter are located in a relatively poor coverage environment. The MTC devices are generally installed in a place with an extremely weak wireless network signal such as an indoor corner or even a basement, and in this case, a coverage enhancement technology is required to implement coverage of the Internet of Things.
Second, the Internet of Things needs to support a large quantity of low-rate devices. A quantity of MTC devices is far greater than a quantity of devices used for communication among people. However, a data packet transmitted by the MTC device is extremely small, and is delay-insensitive.
Third, an Internet of Things device needs to have extremely low costs. Many MTC applications need to obtain and use an MTC device with extremely low costs, so as to facilitate deployment on a large scale.
Fourth, an Internet of Things device needs to feature low energy consumption. In most cases, an MTC device is battery-powered. However, in many cases, the MTC is required to operate properly for more than a decade without a battery change, and this requires that the MTC device can operate with extremely low power consumption.
So far, an expected objective of low costs, wide coverage, and low energy consumption still cannot be achieved. To satisfy these special requirements, in a recent topic of Narrowband Internet of Things (NB-IoT), three NB-IoT operation modes are defined:
(1) Standalone operation (Standalone operation): That is, an independent frequency band, for example, one or more carriers in a Global System for Mobile Communication (GSM) network, is used.
When the standalone operation is used, an NB-IoT uplink-downlink frequency band spacing is the same as a current GSM uplink-downlink frequency band spacing, and therefore no special processing is required.
(2) In-band operation (In-band operation): One or more physical resource blocks (PRB) on a Long Term Evolution (LTE) carrier are used.
Referring to FIG. 1, an LTE downlink carrier frequency is fLTEDL, and an LTE uplink carrier frequency is fLTEUL, and therefore a carrier frequency spacing thereof is |fLTEDL−fLTEUL|. In the LTE downlink carrier frequency, because an intermediate subcarrier of 15 kHz serves as a central direct current (DC) subcarrier and is not used, when the in-band operation is used by the NB-IoT, there is a deviation between an NB-IoT uplink-downlink carrier frequency spacing and the LTE uplink-downlink carrier frequency spacing. As shown in FIG. 1, a left side in the figure shows downlink carrier frequencies, and a right side in the figure shows uplink carrier frequencies. If uplink and downlink physical resource blocks used for uplink NB-IoT transmission have the same indexes as those used in LTE, when an NB-IoT carrier frequency is located on a left side of an LTE center carrier frequency, the NB-IoT uplink-downlink carrier frequency spacing is |fLTEDL−fLTEUL|+7.5 kHz; or when an NB-IoT carrier frequency is located on a right side of an LTE center carrier frequency, the NB-IoT uplink-downlink carrier frequency is |fLTEDL−fLTEUL|−7.5 kHz.
(3) Guard band operation (Guard band operation): An unused resource block in an LTE carrier guard band is used.
Referring to FIG. 2, when the guard band operation mode is used, a problem, similar to that in the in-band operation, that there is a deviation between an NB-IoT uplink-downlink carrier frequency spacing and an LTE uplink-downlink carrier frequency spacing may also exist.
In FIG. 2, Δ1 and Δ2 are NB-IoT uplink-downlink carrier frequency spacings, the LTE uplink-downlink carrier frequency spacing is |fLTEDL−fLTEUL|, and there is a deviation between |fLTEDL−fLTEUL| and each of Δ1 and Δ2.
In addition, if different physical resource blocks are used for an LTE uplink and downlink, there is a deviation between the NB-IoT uplink-downlink carrier frequency spacing and the LTE uplink-downlink carrier frequency spacing.
It may be learned from the foregoing description that because the NB-IoT uplink-downlink carrier frequency spacing is inconsistent with the LTE uplink-downlink carrier frequency spacing, if a terminal continues to use the uplink-downlink carrier frequency spacing defined in the LTE, there is a deviation between an uplink carrier frequency used by the terminal and an actual NB-IoT uplink carrier frequency allocated to the terminal. Consequently, the terminal makes a mistake in determining the NB-IoT uplink carrier frequency, interference to an adjacent frequency band is caused, and available bandwidth is wasted.